Fuse 4 blows

Does it matter on the left lamp, whether the headlight switch is clear off, or in park or headlights? That might indicate a grounding problem

With the problem showing up, that is, with the left lamp lit up, try disconnecting the steering column connector where the TS switch comes out of the column, see if it causes the lamp to go out.

IF THE lamp does go out, find the Light Green wire in that connector on the "car" side (not the column, and ground it with a jumper. If the left lamp comes back on, you are getting a "back feed" from some other circuit.

If it does not, you MAY have a bad TS switch.

With the front lamp lit IE "the problem" showing up, and with the TS switch connector hooked back up, pull out the left front bulb. Take a test lamp or meter and probe for power at the light green wire either at the socket or at the TS switch connector. If you have power there, then you are likely getting power from the TS switch, "a problem."

Once again pull the connector loose, and probe for power at the light green at the "car side" of the connector. No power means it was LIKELY coming from the switch and not a backfeed from somewhere else